In general, a wind-driven electricity generator generates a power upon receipt of a natural wind. For this reason, an output power is greatly influenced by a fluctuation in a wind speed. In order to supply a power generated by the wind-driven electricity generator to a power line (referred to as a “circuit”) of a power company, the wind-driven electricity generator is jointed (linked) to the circuit. However, the fluctuation in the output of the wind-driven electricity generator which is caused by the fluctuation in the wind speed causes a quantity of the power to be supplied to the circuit momentarily.
In the circuit, a power in an equal quantity to that of a power to be consumed should be supplied at the same time. For this reason, the power company predicts a time variation in the consumed power to be changed momentarily and makes a power supplying plan to the circuit in conformity therewith. In order to easily implement the power supplying plan, an unstable power having a non-constant output cannot be permitted to flow into the circuit. In the case in which a wind-driven electricity generation system for linking a wind-driven electricity generator to a circuit is introduced, it is required to suppress a fluctuation in a power output to a circuit.
In order to suppress the fluctuation in the power output to the circuit, conventionally, there is proposed a wind-driven electricity generator of a type having a storage battery. The wind-driven electricity generator of a type having a storage battery uses a part of a power generated by the wind-driven electricity generator for a power storage to control a charge and discharge so that an almost constant power can be supplied to the circuit without an influence by an air quantity. There are some wind-driven electricity generators for charging/discharging a storage battery to cancel a fluctuation in a quantity of power generation through the wind-driven electricity generator with respect to a target power quantity to be made constant and supplying, to a circuit, a power obtained by synthesizing a power generation quantity of the wind-driven electricity generator and charging/discharging quantities of the storage battery, thereby suppressing a fluctuation in the output power of the wind-driven electricity generator as seen from the circuit (for example, see Patent Documents 1 to 3).
Moreover, there is also proposed a wind-driven electricity generation system for predicting a wind condition to smooth an output power of a wind-driven electricity generator (for example, see Patent Documents 4 and 5). The wind-driven electricity generation system described in the Patent Documents 4 and 5 predicts a quantity of power generation in the near future from the output power of the wind-driven electricity generator through a calculation to control a charge and discharge of a storage battery by setting the predicted quantity of power generation to be a reference (target). In other words, when the quantity of power generation of the wind-driven electricity generator is larger than the predicted quantity of power generation, an excessive part is charged into the storage battery. On the other hand, when the quantity of power generation is smaller than the predicted quantity of power generation, an insufficient part is discharged from the storage battery and the quantity of power generation of the wind-driven electricity generator is synthesized with the quantity of the charge and discharge of the storage battery. Consequently, a fluctuation in the output power of the wind-driven electricity generator is suppressed to draw a curve obtained by smoothing a locus of the quantity of an output power.
Patent Document 1: Japanese Laid-Open Patent Publication No. 11-299106
Patent Document 2: Japanese Laid-Open Patent Publication No. 2000-308370
Patent Document 3: Japanese Laid-Open Patent Publication No. 2003-333752
Patent Document 4: Japanese Laid-Open Patent Publication No. 2004-289896
Patent Document 5: Japanese Laid-Open Patent Publication No. 2004-301116